Troubleshooting Pim Configuration - 3Com Switch 4800G 24-Port Configuration Manual

Troubleshooting PIM
Configuration
Failure of Building a
Multicast Distribution
Tree Correctly
(10.110.5.100, 232.1.1.1)
Protocol: pim-ssm, Flag:
UpTime: 00:13:25
Upstream interface: Vlan-interface101
Upstream neighbor: 192.168.1.2
RPF prime neighbor: 192.168.1.2
Downstream interface(s) information:
Total number of downstreams: 1
1: Vlan-interface100
Protocol: igmp, UpTime: 00:13:25, Expires: -
The information on Switch B and Switch C is similar to that on Switch A.
# View the PIM routing table information on Switch D.
[SwitchD] display pim routing-table
Total 0 (*, G) entry; 1 (S, G) entry
(10.110.5.100, 232.1.1.1)
Protocol: pim-ssm, Flag:LOC
UpTime: 00:12:05
Upstream interface: Vlan-interface300
Upstream neighbor: NULL
RPF prime neighbor: NULL
Downstream interface(s) information:
Total number of downstreams: 1
1: Vlan-interface105
Protocol: pim-ssm, UpTime: 00:12:05, Expires: 00:03:25
Symptom
None of the routers in the network (including routers directly connected with
multicast sources and receivers) has multicast forwarding entries. That is, a
multicast distribution tree cannot be built correctly and clients cannot receive
multicast data.
Analysis
When PIM-DM runs on the entire network, multicast data is flooded from the
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first hop router connected with the multicast source to the last hop router
connected with the clients along the SPT. When the multicast data is flooded to
a router, no matter which router is, it creates (S, G) entries only if it has a route
to the multicast source. If the router does not have a route to the multicast
source, or if PIM-DM is not enabled on the router's RPF interface to the
multicast source, the router cannot create (S, G) entries.
When PIM-SM runs on the entire network, and when a router is to join the SPT,
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the router creates (S, G) entries only if it has a route to the multicast source. If
the router does not have a router to the multicast source, or if PIM-DM is not
enabled on the router's RPF interface to the multicast source, the router cannot
create (S, G) entries.
When a multicast router receives a multicast packet, it searches the existing
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unicast routing table for the optimal route to the RPF check object. The
outgoing interface of this route will act as the RPF interface and the next hop
will be taken as the RPF neighbor. The RPF interface completely relies on the

Troubleshooting PIM Configuration

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